Piezoelectric device, ink-jet printing head, and method for manufacturing same, and printer

ABSTRACT

A piezoelectric device includes an adhesive layer composed of a material which enhances adhesion between a base plane of a piezoelectric device and a lower electrode, a diffusion preventing layer formed with a material which prevents the phenomenon of diffusion of a component of the adhesive layer into the lower electrode, wherein the lower electrode is formed over the diffusion preventing layer, a piezoelectric film formed over the lower electrode and exhibits an electromechanical transducing action, and an upper electrode formed over the lower electrode. The diffusion preventing layer prevents diffusion of titanium which is a principal component of the adhesive layer.

TECHNICAL FIELD

The present invention relates to a piezoelectric device used for an inkjet printing head. Particularly, this-invention relates to a techniquefor preventing impurities from diffusing in a lower electrode or apiezoelectric film upon baking the piezoelectric film.

BACKGROUND ART

An ink jet printing head used for an ink jet printer, which obtainsletters or desired images by discharging ink drops onto printing paperselectively in accordance with print data to be input, comprises apiezoelectric device which functions as a drive source for dischargingink. The piezoelectric device comprises a piezoelectric film heldbetween an upper electrode and a lower electrode.

A silicon dioxide film which is superior mainly as a diaphragm is usedas a base plane for forming the piezoelectric device. Since the silicondioxide film has bad adhesion with a metal of a lower electrode for thepiezoelectric device, an adhesive layer made of titanium is oftenemployed between the diaphragm and the lower electrode.

Platinum is often used for the lower electrode. When the piezoelectricfilm is formed over a non-oriented film in an amorphous state such assilicon oxide, orientation of the piezoelectric film is disturbed,thereby impairing ferroelectricity. With this regard, it is acharacteristic of platinum that it becomes an oriented film even if itis formed over a non-oriented film. Accordingly, the piezoelectric filmis made oriented by using platinum for the lower electrode and bycomposing the piezoelectric film to be formed over the lower electrode.

As metals, other than platinum, used for the lower electrode, forexample, U.S. Pat. No. 5,122,923, U.S. Pat. No. 5,191,510, an officialgazette of Japanese Laid-Open (Kokai) Publication No. Hei 7-245236, andan official gazette of Japanese Laid-Open (Kokai) Publication No. Hei7-24523 disclose an alloy of platinum and iridium, iridium, and iridiumoxide. These metals are used mainly for the purpose of enhancing theproperties of dielectrics and preventing any deterioration with age.

However, methods of using the above-described conventional materialscause various inconveniences.

For example, in the lower electrode, titanium composing the adhesivelayer diffuses in, and forms an alloy with, platinum composing the lowerelectrode upon baking a PZT-type piezoelectric precursor film, therebylowering the piezoelectric properties.

FIG. 10 shows a diffusion ratio of titanium, which is a principalcomponent of the adhesive layer, in platinum which is a principalcomponent of the lower electrode, upon baking the piezoelectricprecursor film. The horizontal axis indicates lengths of the lowerelectrode and the adhesive layer in a film thickness direction, and thevertical axis indicates respective contents of platinum and titanium inpercentage. Measurement was conducted by setting the thickness of thelower electrode as 500 nm and the thickness of the adhesive layer as 20nm. About 30% titanium is mixed in the lower electrode in the vicinityof an interface between the lower electrode and the adhesive layer.About 5% titanium is mixed at an interface between the lower electrodeand the piezoelectric film, which is 500 nm apart from the interfacebetween the lower electrode and the adhesive layer. It can be confirmedthat, in the lower electrode, platinum and titanium are alloyed unevenlywith respect to the film thickness direction and the orientation ofcolumnar crystals of platinum is disturbed. Such a phenomenon causesdisturbance of orientation of the piezoelectric film formed over thelower electrode, thereby giving rise to problems such as lowering of thepiezoelectric properties of the piezoelectric device. Moreover, astitanium is mixed unevenly in platinum, physical properties of the lowerelectrode in the thickness direction change. Such a lower electrodemakes designing and processing difficult.

Concerning the piezoelectric film, thermal treatment at the time ofbaking causes titanium to diffuse in the piezoelectric film through thelower electrode, and the existence of titanium in the piezoelectric filmdeteriorates the piezoelectric properties of the piezoelectric device.This is because the existence of titanium disturbs a stoichiometricratio in a composition of the piezoelectric film and a layer of lowdielectric constant is generated at an interface between the lowerelectrode and the piezoelectric film.

On the other hand, it is also indicated that when iridium is used forthe lower electrode, a leak current considerably increases (as in“Clarification of Leak Mechanism of PZT Capacitor Accumulated on IrElectrode” from lecture proceedings for the 59^(th) Applied PhysicsSociety Symposium (published on Sep. 15, 1998), p. 450).

SUMMARY OF THE INVENTION

In consideration of various problems described above, it is a firstobject of this invention to make it possible to prevent the diffusion ofimpurities in the piezoelectric film or the lower electrode at the timeof manufacture, and to provide a piezoelectric device of highreliability, which will not peel off, and a method for manufacturingsuch a piezoelectric device.

It is a second object of this invention to provide an ink jet printinghead which uses such a piezoelectric device, and to provide a method formanufacturing such an ink jet printing head.

It is a third object of this invention to provide a printer which usessuch an ink jet printing head.

The present invention is a piezoelectric device exhibiting anelectromechanical transducing action, characterized in that itcomprises:

an adhesive layer composed of a material which enhances adhesion betweena base plane of the piezoelectric device and a lower electrode of thepiezoelectric device;

a diffusion preventing layer composed of a material which prevents aphenomenon of diffusion of a component of the adhesive layer into theelectrode;

a lower electrode formed over the diffusion preventing layer;

a piezoelectric film which is formed over the lower electrode and whichexhibits the electromechanical transducing action; and

an upper electrode formed over the piezoelectric film so as to be pairedwith the lower electrode.

This invention is a piezoelectric device exhibiting an electromechanicaltransducing action, characterized in that it comprises:

an adhesive layer composed of a material which enhances adhesion betweena base plane of the piezoelectric device and a lower electrode of thepiezoelectric device;

a lower electrode formed over the adhesive layer;

a diffusion preventing layer formed over the lower electrode andcomposed of a material which prevents a phenomenon of diffusion of acomponent of the adhesive layer into the piezoelectric film and alsoprevents a phenomenon of diffusion of a component of the piezoelectricfilm into the lower electrode;

a piezoelectric film which is formed over the diffusion preventing layerand which exhibits the electromechanical transducing action; and

an upper electrode formed over the piezoelectric film so as to be pairedwith the lower electrode.

The diffusion preventing layer is an alloy of titanium and one deviceselected from a group consisting of iridium, palladium, rhodium,ruthenium, and osmium.

The adhesive layer contains, as its principal component, one deviceselected from a group consisting of titanium and chromium.

The lower electrode is composed of platinum as its principal component.

This invention is an ink jet printing head comprising the piezoelectricdevice of this invention, as a piezoelectric actuator, over a diaphragmwhich serves as the base plane.

The diaphragm has a laminated structure of silicon dioxide and zirconiumoxide.

This invention is a printer comprising the ink jet printing head of thisinvention as printing means.

This invention is a method for manufacturing a piezoelectric deviceexhibiting an electromechanical transducing action, characterized inthat it comprises:

an adhesive layer forming step of forming, over a base plane of thepiezoelectric device, an adhesive layer with a material which enhancesadhesion between the base plane and a lower electrode of thepiezoelectric device;

a diffusion preventing layer forming step of forming, over the adhesivelayer, a diffusion preventing layer with a material which prevents aphenomenon of diffusion of a component of the adhesive layer into theelectrode;

a lower electrode forming step of forming, over the diffusion preventinglayer, a lower electrode by using a conductive material;

a piezoelectric film forming step of forming, over the lower electrode,a piezoelectric film by using a piezoelectric material; and

an upper electrode forming step of forming, over the piezoelectric film,an upper electrode by using a conductive material.

This invention is a method for manufacturing a piezoelectric deviceexhibiting an electromechanical transducing action, characterized inthat it comprises:

an adhesive layer forming step of forming, over a base plane of thepiezoelectric device, an adhesive layer with a material which enhancesadhesion between the base plane and a lower electrode of thepiezoelectric device;

a lower electrode forming step of forming, over the adhesive layer, alower electrode by using a conductive material;

a diffusion preventing layer forming step of forming, over the lowerelectrode, a diffusion preventing layer with a material which prevents aphenomenon of diffusion of a component of the adhesive layer into thepiezoelectric film, and which also prevents a phenomenon of diffusion ofa component of the piezoelectric film into the lower electrode;

a piezoelectric film forming step of forming, over the diffusionpreventing layer, a piezoelectric film by using a piezoelectricmaterial; and

an upper electrode forming step of forming, over the piezoelectric film,an upper electrode by using a conductive material.

The diffusion preventing layer forming step is the step of forming thediffusion preventing layer by using, as its principal component, onedevice selected from a group consisting of iridium, palladium, rhodium,ruthenium, and osmium as starting materials.

The adhesive layer forming step is the step of forming the adhesivelayer by using, as its principal component, one device selected from agroup consisting of titanium and chromium.

The lower electrode forming step is the step of forming the lowerelectrode by using platinum as its material.

The piezoelectric film forming step is the step including a thermaltreatment step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a piezoelectric device of Embodiment 1.

FIGS. 2A-2C show steps (1) of manufacturing an ink jet printing head ofEmbodiment 1.

FIGS. 3A-3F show steps (2) of manufacturing the ink jet printing head ofEmbodiment 1.

FIGS. 4A-4I show steps (3) of manufacturing the ink jet printing head ofEmbodiment 1.

FIG. 5 is a variation example of the ink jet printing head of Embodiment1.

FIG. 6 is a graph indicating a contamination ratio of titanium in alower electrode in the case of Embodiment 1.

FIG. 7 is an exploded perspective view of the ink jet printing head ofthis invention.

FIG. 8 is a sectional view of a principal part of the ink jet printinghead of this invention.

FIG. 9 is a perspective view of a printer of this invention, explainsthe structure of the printer.

FIG. 10 is a graph indicating a contamination ratio of titanium in aconventional lower electrode.

FIG. 11 is a sectional view of a piezoelectric device of Embodiment 2.

FIG. 12 is a sectional view of a piezoelectric device of Embodiment 3.

FIGS. 13A-13C show steps (1) of manufacturing an ink jet printing headof Embodiment 3.

FIGS. 14A-14F show steps (2) of manufacturing an ink jet printing headof Embodiment 3.

FIG. 15 is a graph indicating a contamination ratio of titanium in thelower electrode in the case of Embodiment 3.

FIG. 16 is a typical diagram of a TEM photograph of an interface betweena diffusion preventing layer and a piezoelectric film of the examples.

BEST MODE FOR CARRYING OUT THE INVENTION

The best mode for carrying out this invention is hereinafter explainedwith reference to the attached drawings. In the following descriptions,the same reference numeral indicates the same composition or the samename.

Embodiment 1

Embodiment 1 of this invention relates to a piezoelectric device, an inkjet printing head, and a printer in which a diffusion preventing layeris newly provided between a lower electrode and an adhesive layer.

FIG. 1 is a sectional view of a piezoelectric device of this embodiment,which describes the structure of the piezoelectric device. Apiezoelectric device 40 of Embodiment 1 is composed by laminating, overa diaphragm which forms a base plane, an adhesive layer 401, a diffusionpreventing layer 402, a lower electrode 403, a piezoelectric film 404,and an upper electrode 405.

The adhesive layer 401 is composed of a material which enhances adhesionbetween the base plane of the piezoelectric device and the lowerelectrode of the piezoelectric device. The adhesive layer 401 contains,as its principal component, one device selected from a group consistingof titanium and chromium. The adhesive layer 401 is formed with athickness approximately in the range of 10 nm to 50 nm.

The diffusion preventing layer 402 is formed with a material whichprevents components of the adhesive layer from diffusing into theelectrode. The diffusion preventing layer 402 is an alloy of titaniumand one device selected from a group consisting of iridium, palladium,rhodium, ruthenium, and osmium. The diffusion preventing layer preventstitanium, which is a principal component of the adhesive layer 401, fromdiffusing into the lower electrode 403 upon baking a piezoelectricprecursor film by applying thermal treatment such as a sol-gel method.However, it is also possible to apply other devices to the diffusionpreventing layer as long as they have physico-chemical propertiessimilar to those of the above-listed devices. The diffusion preventinglayer 402 is formed with a thickness approximately in the range of 20 nmto 150 nm.

The lower electrode 403 is formed with a conductive material over thediffusion preventing layer 402 and is opposed to the upper electrode405. Application of voltage between the two electrodes makes it possibleto cause an electromechanical transducing action at the piezoelectricfilm 404. The lower electrode 403 is composed particularly by containingplatinum as its principal component. The lower electrode is formed witha given thickness (approximately from 0.1 μm to 0.5 μm).

The piezoelectric film 404 is a crystal film of a perovskite structure,which is formed over the lower electrode 403 and which is made offerroelectric ceramic materials, such as PZT, that exhibits anelectromechanical transducing action. As examples of materials for thepiezoelectric film 404, ferroelectric piezoelectric materials such aslead zirconate titanate (PZT), and such other materials obtained byadding metallic oxide such as niobium oxide, nickel oxide or magnesiumoxide to the above-mentioned ferroelectric ceramic materials arepreferred. Specifically, lead titanate (PbTiO₃), lead zirconate titanate(Pb(Zr,Ti)O₃), lead zirconate (PbZrO₃), lead lanthanum titanate((Pb,La)TiO₃), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O₃), orlead magnesium neobate zirconium titanate (Pb (Zr,Ti)(Mg,Nb)O₃) can beused. Concerning the thickness of the piezoelectric film 404, thethickness is limited to a degree whereby cracks will not be generated inthe manufacturing steps, and the piezoelectric film is formed with sucha thickness as will exhibit sufficient displacement properties. Forexample, the piezoelectric film 404 is made with a thicknessapproximately in the range of 1 μm to 2 μm.

The upper electrode 405 is a conductive film formed with a giventhickness (approximately 0.1 μm) by using materials such as gold,platinum, or iridium.

An explanation is hereinafter given about a structure of an ink jetprinting head which comprises the piezoelectric device 40 as apiezoelectric actuator. As shown in a partly sectional perspective viewof the principal part of FIG. 7 and in an exploded perspective view ofFIG. 8, an ink jet printing head 1 is composed by placing a nozzle plate10, a substrate 30 and the piezoelectric device 40 in a housing 50.

On a pressure chamber substrate 20, pressure chambers (cavities) 21,side walls (partitions) 22, supply ports 24, and a reservoir 23 areformed by etching a silicon substrate. The pressure chambers 21 arespaces for storing ink or the like to be discharged. The side walls 22are formed to partition the pressure chambers 21. The reservoir 23 formsa common channel to fill the respective pressure chambers 21 with ink.The supply ports 24 are formed so as to be capable of introducing inkfrom the reservoir 23 to the respective pressure chambers 21.

A diaphragm 30 is formed on one side of the pressure chamber substrate20, and the piezoelectric devices 40 are provided on the diaphragm 30 atpositions corresponding to those of the pressure chambers 21. As thediaphragm 30, an oxide film (silicon dioxide film) is appropriatebecause it has elasticity, mechanical strength and insulationperformance. However, the diaphragm 30 is not limited to an oxide film,and a zirconium oxide film, a tantalum oxide film, a silicon nitridefilm, or an aluminum oxide film may also be used. An ink tank port 35 isprovided at a part of the diaphragm 30 so that it is possible to conductink stored in an ink tank (not shown) into the pressure chambersubstrate 20. The lower electrode may be made to serve also as thediaphragm by forming the lower electrode 402 and the adhesive layer 401on the entire surface of the diaphragm 30.

A nozzle plate 10 is mounted on the side of the pressure chambersubstrate 20 as opposed to the diaphragm 30. In the nozzle plate 10,nozzles 11 are located at positions corresponding to the respectivepressure chambers 21.

The above-described structure of the ink jet printing head is oneexample, and the piezoelectric device 40 can be applied to any piezo jetheads for which the piezoelectric device can be used as a piezoelectricactuator.

With the structure of the ink jet printing head 1, if voltage is appliedbetween the electrodes and the piezoelectric device 40 is thendistorted, the diaphragm 30 deforms in accordance with such distortion.Such deformation gives pressure to ink in the pressure chamber 21, andthe ink is thereby discharged from the nozzle 11.

FIG. 9 is a perspective view of a printer which comprises the ink jetprinting head 1 as ink discharging means. As shown in FIG. 9, thisprinter 100 has a tray 3 and an outlet 4 provided on a printer main body2. The main body 2 has the ink jet printing head 1 of this inventionbuilt therein. In the main body 2, the ink jet printing head 1 islocated so as to enable its reciprocating movement over and across paper5 supplied from the tray 3 by a paper feeding mechanism (not shown). Theoutlet 4 is an outlet capable of ejecting paper 5 on which printing hasbeen completed.

Manufacturing Method

An explanation is hereinafter given about a method for manufacturing apiezoelectric device and an ink jet printing head of this invention.FIGS. 2 through 4 described below are sectional views of thepiezoelectric device as taken along lines A—A of FIGS. 7 and 8, whichare illustrative of the manufacturing steps.

Adhesive Layer Forming Step (FIG. 2A):

This step is the step of forming, over the base plane of thepiezoelectric device 40, the adhesive layer 401 by using a materialwhich will enhance adhesion between the base plane and the lowerelectrode of the piezoelectric device.

The diaphragm 30 which serves as the base plane is formed by causingoxidation over a silicon single crystal substrate 20 of a given size andthickness (for example, 150 mm in diameter and 600 μm thick) by athermal oxidation method. The thermal oxidation is to givehigh-temperature treatment in an oxidizing atmosphere containing oxygenor water vapor. As another method, a CVD method may be employed. As aresult of this step, the diaphragm 30 made of silicon dioxide is formedwith a thickness of about 1 μm.

As the diaphragm 30, a zirconium oxide film, a tantalum oxide film, asilicon nitride film, an aluminum oxide film or the like may be usedinstead of the oxide film. Alternatively, a zirconium oxide film, atantalum oxide film, an aluminum oxide film or the like may be laminatedover the oxide film.

Subsequently, a titanium film which becomes the adhesive layer 401 isformed with a thickness of, for example, 10 nm by a sputtering methodover the surface of the diaphragm 30 on the side where the piezoelectricdevice is to be formed. As the adhesive layer 401, chromium can be usedinstead of titanium.

Diffusion Preventing Layer Forming Step (FIG. 2B):

This step is the step of forming, over the adhesive layer 401, adiffusion preventing layer 402 by using a material which will prevent aphenomenon of diffusion of a component of the adhesive layer into theelectrode.

The diffusion preventing layer 402 made of iridium is formed with athickness of about 100 nm over the surface of the adhesive layer 401 bymeans of, for example, a sputtering method. As stated above, other thaniridium, palladium, rhodium, ruthenium, osmium or the like may be used.

Lower Electrode and Piezoelectric Film Forming Step (FIG. 2C):

This step is the step of forming a lower electrode 403 by using aconductive material over the diffusion preventing layer 402, and offorming a piezoelectric film 404 by using a piezoelectric material overthe lower electrode 403.

A platinum film is made with a thickness of, for example, 200 nm by asputtering film forming method to form the lower electrode 403 over thesurface of the diffusion preventing layer 402.

A piezoelectric precursor film is laminated over the surface of thelower electrode 403. For example, if a sol-gel method is employed, aPZT-type piezoelectric film precursor (sol) is used, concerning which amole mixing ratio of lead titanate to lead zirconate is 44%:56%. Theprecursor is applied with a uniform thickness. Application of the sol isperformed by utilizing conventional techniques such as a spin coatingmethod, a dip coating method, a roll coating method, and a bar coatingmethod. The applied precursor is dried at a given temperature and isthen pyrolyzed. The drying step is performed by means of natural dryingor by heating at a temperature of 200° C. or lower. The pyrolyzing stepis performed by gelling the precursor film and heating it at atemperature sufficient to remove organic substances from the film andfor a sufficient period of time. As a result of this step, a porous gelfilm is obtained, which is made of amorphous metallic oxide which doesnot substantially contain any residual organic substances. These stepsof coating, drying and pyrolyzing are repeated for a certain number oftimes, for example, ten times until the thickness in the range of 0.8 μmto 2.0 μm is achieved. Concerning the piezoelectric precursor filmformed in the above-described manner, if the sol composition is adjustedso that X and Y in a composition formula represented byPb_(x)Ti_(y)Zr_(z)O₃(Y+Z=1) become in the range of 1.00≦×≦1.20 and0.4≦Y≦0.6, it is possible to provide the piezoelectric film aftercrystallization with practicable piezoelectric properties. Obviously,other ferroelectric materials mentioned above can also be used.

Subsequently, the entire substrate is heated after the fifth and tenthpyrolysis in order to crystallize the piezoelectric precursor film. Forexample, an infrared radiation light source (not shown) is used to heatthe substrate from its both sides in an oxygen atmosphere by keeping atemperature of 650° C. for five minutes and then heating at atemperature of 900° C. for one minute, and the substrate is then left tocause the temperature to naturally decrease. As a result of this step,the piezoelectric precursor film crystallizes and sinters in theabove-described composition, thereby becoming the piezoelectric film 404having a perovskite crystal structure.

In the thermal treatment of this piezoelectric film 404, titanium of theadhesive layer 401 oxidizes and diffuses. This diffusion causes a changeof the diffusion preventing layer 402 into the mixed state of iridium,which has hardly oxidized, and titanium oxide. The layer in such a stateis called “alloy” in this specification. The diffusion preventing layer402 made of this Ir-Ti alloy prevents titanium from diffusing into thepiezoelectric film 404 and also prevents oxygen in the piezoelectricfilm 404 from escaping toward the side of the lower electrode at thetime of baking. This action of the diffusion preventing layer 402 canprevent the generation of a low dielectric constant layer due to achange in the stoichiometric ratio of the piezoelectric film 404.

As for the method for manufacturing the piezoelectric film 404, a highfrequency sputtering film-forming method, a CVD method, an MOD method, alaser ablation method or the like can be employed other than the sol-gelmethod.

When the piezoelectric film 404 is formed by the sputtering method, apiezoelectric precursor film in an amorphous state is formed over thelower electrode by means of sputtering by using a PZT sintered body ofgiven components as a target. This piezoelectric precursor film in theamorphous state is heated to cause sintering and crystallization. Thissintering treatment is performed by heating the piezoelectric precursorfilm in an oxygen atmosphere (for example, in oxygen or in a mixed gasof oxygen and inert gas such as argon) at a temperature in the range of500° C. to 700° C. In this step, the piezoelectric precursor filmbecomes the piezoelectric film 40 with a crystal particle diameterranging from 0.005 μm to 0.4 μm.

Moreover, a film of iridium may be formed over the lower electrode 403.This film is formed with a thickness of, for example, 20 nm by thesputtering method. Intervention of the iridium layer between the lowerelectrode 403 and the piezoelectric film 404 can efficiently preventoxygen from escaping from the piezoelectric film 404. This makes itpossible to prevent aged deterioration of ferroelectricity of thepiezoelectric film 404.

Upper Electrode Forming Step (FIG. 3A):

This step is the step of forming, over the piezoelectric film 404, anupper electrode 405 by using a conductive material. For example, iridiumis used as the conductive material to form, by the sputtering method,the upper electrode 405 with a thickness of about 100 nm.

The layer structure of the piezoelectric device 40 is completed throughthe above-described steps. Molding is performed by etching this layerstructure in an appropriate shape in order to use it as thepiezoelectric device. In the following steps, this layer structure ismolded into a shape as a piezoelectric actuator and, at the same time, astructure necessary for an ink jet printing head is formed.

Dry Etching Step (FIG. 3B):

A resist with a uniform film thickness is applied over the upperelectrode 405 at corresponding positions where pressure chambers of thesubstrate 20 are to be formed. As an applying method, any appropriatemethod such as a spinner method or a spray method is utilized. After theapplication of the resist, exposure and development are conducted toleave the resist in a shape corresponding to the shape of thepiezoelectric actuators. The resist is used as a mask to perform dryingetching on the upper electrode 405, the piezoelectric film 404, thelower electrode 403, the diffusion preventing layer 402, and theadhesive layer 401, thereby forming the piezoelectric devices 20corresponding to the representative pressure chambers. Dry etching isperformed by selecting, as appropriate, a gas which exhibits selectivityregarding the respective layer materials.

If the lower electrode 403 is made to function also as a part of thediaphragm, as shown in FIG. 5, it is possible to adjust itsdiaphragmatic strength by adjusting the film thickness of an area 50,which is a bridge between the piezoelectric device 40 and side walls 22,by changing the depth of etching.

Together with the above step, a protective film made of silicon dioxideis formed by employing a CVD method or the like on the side of thesubstrate 20 where the piezoelectric devices 20 are formed. Since thepiezoelectric devices are already formed, it is necessary to form thefilm at such a temperature that will not influence the piezoelectricdevices. After the formation of the protective film, an oxide film 30 onthe pressure chamber side of the substrate 20 is etched with hydrogenfluoride or the like in areas including at least pressure chambers 21 orside walls 22, thereby forming an opening 50.

Wet Etching Step (FIG. 3C):

A wet anisotropy etchant, for example, an aqueous potassium hydroxidesolution (concentration: 10%) with its temperature retained at 80° C. isused to etch the area of the opening 50 until a given depth is obtained.Instead of wet etching, anisotropy etching using active gas, such asparallel plane plate reactive ion etching, may be employed. As a resultof this step, a concave 51 is formed in the substrate 20.

Oxide Film Forming Step (FIG. 4A):

A chemical vapor phase epitaxy method such as a CVD method is employedon the concave 51 to form an oxide film 302 as an etching protectivelayer in accordance with the shapes of the pressure chambers 21.

Pressure Chamber Forming Step (FIG. 4B):

An anisotropy etchant, for example, an aqueous potassium hydroxidesolution (concentration: 10%) with its temperature retained at 80° C. isused to perform anisotropy etching of the substrate 20 from the pressurechamber side toward the piezoelectric device side. As a result of thisstep, the pressure chamber 21 portions are etched, thereby forming theside walls 22.

Nozzle Plate Adhering Step (FIG. 4C):

A nozzle plate 10 is adhered to cover the pressure chambers 21 of thepressure substrate 20 formed in the above-described steps. As anadhesive used therefor, any adhesive of epoxy type, urethane type,silicon type or the like can be used.

As for the shape formed by the pressure chamber substrate 20 and thenozzle plate 10, they may be formed integrally by etching a siliconsingle crystal substrate.

EXAMPLE 1

As an example of the piezoelectric device manufactured through theabove-described manufacturing steps, FIG. 6 shows the results of anexamination of titanium content in the lower electrode. In FIG. 6, thehorizontal axis indicates a thickness direction of the lower electrode.The origin is set at an interface between the adhesive layer and thediffusion preventing layer. The vertical axis indicates respectivecontents of titanium, iridium and platinum in percentage. It is apparentfrom FIG. 6 that about 40% titanium is contained at the interfacebetween the adhesive layer and the diffusion preventing layer, iridiumand titanium are alloyed, and there is little diffusion of titanium intothe lower electrode.

According to Embodiment 1, it is possible to prevent the phenomenon ofdiffusion of titanium, which is the principal component of the adhesivelayer, into the lower electrode at the time of baking of thepiezoelectric precursor film. Thus, it is possible to maintain theorientation of the lower electrode in a good state. If a ferroelectricceramic material such as lead zirconate titanate is used as theferroelectric material (piezoelectric film), the molecular structure inthe amorphous state at the time of baking of the piezoelectric filmdevelops to a compact perovskite crystal structure. The orientation atthe time of crystallization of the piezoelectric film depends upon theorientation of the lower electrode. Since the lower electrode isoriented well in this embodiment, it is possible to crystallize thepiezoelectric film with good orientation. Since the crystal structurewhich is oriented anisotropically plays a key role in the transductionof electric energy and mechanical energy, this results in theenhancement of the piezoelectric properties of the piezoelectric device.

EXAMPLE 2

The piezoelectric device was manufactured by the manufacturing method ofthis embodiment by changing the thickness of the lower electrode, thethickness of the piezoelectric film, the number of times of baking andso on. Table 1 shows the results of measurement of adhesive strengthbetween the lower electrode and the substrate in the piezoelectricdevice. However, a lamination structure of the manufacturedpiezoelectric device is a layer structure composed of the upperelectrode (Pt), the piezoelectric film (PZT), the lower electrode (Pt),the diffusion preventing layer (Ir-Ti), and the substrate. As acomparison, a piezoelectric device having a layer structure without thediffusion preventing layer (the structure composed of the upperelectrode (Pt), the piezoelectric film (PZT), the lower electrode (Pt),the adhesive layer (Ti), and the substrate) was used.

TABLE 1 Film Thickness Thickness of Number of of Lower PiezoelectricTimes of Adhesive Electrode Film Baking strength Example 500 nm 0.8 μm 219.6 mN Comparison 500 nm 0.8 μm 2 17.8 mN Example 500 nm 1.2 μm 4 19.0mN Comparison 500 nm 1.2 μm 4 14.2 mN Example 500 nm 1.2 μm 4 19.1 mNComparison 500 nm 1.2 μm 4. 9.8 mN

Table 2 shows the results of measurement of a breakdown voltage and apiezoelectric constant d₃₁ when the thickness of the piezoelectric filmof this example was changed.

TABLE 2 Thickness of Piezoelectric Breakdown Film Voltage d₃₁ at 15V d₃₁at 25V Example 0.8 μm 54V 201 pC/N 179 pC/N Comparison 0.8 μm 41V 178pC/N 161 pC/N Example 1.2 μm 89V 244 pC/N 199 pC/N Comparison 1.2 μm 62V191 pC/N 170 pC/N

As can be seen from Table 2, the breakdown voltage and the piezoelectricconstant d₃₁ of this example are larger than those of the comparison.This is because a low dielectric constant layer does not exist at theinterface between the lower electrode and the piezoelectric film in thepiezoelectric device of this example.

The value of the piezoelectric constant d₃₁ varies depending on themeasured voltage because there is a tendency of the piezoelectricconstant d₃₁ to decrease as the electric field becomes higher. It iseffective to increase the thickness of the piezoelectric film in orderto enhance the properties of the piezoelectric device. However, it isnot desirable to make the thickness of the piezoelectric film too large,because the displacement efficiency lowers. A desirable thickness of thepiezoelectric film for an ink jet printing head of high resolution is inthe range of approximately 1 μm to 2 μm.

Embodiment 2

Embodiment 2 of this invention relates to a variation of the diaphragmstructure of the ink jet printing head.

FIG. 11 is a sectional view of a principal part of an ink jet printinghead of Embodiment 2. The ink jet printing head of Embodiment 2 isdifferent from Embodiment 1 in that the diaphragm of Embodiment 2 has alamination structure of a silicon dioxide film and a zirconium oxidefilm. As shown in FIG. 11, the diaphragm of this embodiment comprises anoxide film 30 and a zirconium oxide (ZrO₂) film 31.

A method for manufacturing this diaphragm is hereinafter explained. Afilm forming method such as a thermal oxidation method or a CVD methodis employed to form a silicon dioxide film (oxide film 30), which is 1μm, over a silicon single crystal substrate. Over this silicon dioxidefilm, a zirconium Zr film is formed with an appropriate thickness (forexample, about 400 nm) by a film forming method such as a sputteringmethod or a vacuum deposition method. High-temperature treatment isgiven to this film in an oxygen atmosphere. When zirconium is oxidized,it becomes a zirconium oxide film 31.

In the above-described structure, the zirconium film is formed as acrystalline layer. It is known that a crystalline layer exhibits betteradhesion than an amorphous layer. Concerning the zirconium oxide film31, its adhesion with the electric device 40 is enhanced.

It has been experimentally confirmed in experiments that if thezirconium film 31 is used as the diaphragm, vibrating properties of thepiezoelectric device are enhanced as compared to the piezoelectricdevice which does not use zirconium for the diaphragm.

According to Embodiment 2, because zirconium is used as a part of thediaphragm, it is possible to enhance the adhesion between thepiezoelectric device and the substrate. Since zirconium is used, it ispossible to enhance the piezoelectric properties of the piezoelectricdevice.

Embodiment 3

Embodiment 3 of this invention relates to a piezoelectric device with adiffusion preventing layer newly provided between a lower electrode anda piezoelectric film.

FIG. 12 is a sectional view illustrative of a structure of apiezoelectric device of this embodiment. A piezoelectric device 41 ofEmbodiment 3 is composed by laminating, over a diaphragm 30 which formsa base plane, an adhesive layer 401, a lower electrode 403, a diffusionpreventing layer 402, a piezoelectric film 404, and an upper electrode405. Embodiment 3 is different from Embodiment 1 in that the diffusionpreventing layer 402 is located between the lower electrode 403 and thepiezoelectric film 404. However, the diffusion preventing layer 402 maybe provided between the adhesive layer 401 and the lower electrode 403.In this case, the piezoelectric device will also exhibit theworking-effect of Embodiment 1.

Compositions and thicknesses of the respective layers are similar tothose of Embodiment 1 and, therefore, descriptions thereof are omitted.

A structure of an ink jet printing head, which comprises thispiezoelectric device 41 as a piezoelectric actuator, a method formanufacturing such an ink jet printing head, a structure of a printer,which comprises this ink jet printing head as printing means, and amethod for manufacturing such a printer are similar to those ofEmbodiment 1 and, therefor, descriptions thereof are omitted.

A method for manufacturing the piezoelectric device of this invention ishereinafter explained. FIGS. 13 and 14 explained below are sectionalviews of the piezoelectric device as taken along lines A—A of FIGS. 7and 8, which are illustrative of the manufacturing steps.

Diaphragm Forming Step and Adhesive Layer Forming Step (FIGS. 13A and13B):

These steps are the steps of forming, over a substrate 20, a diaphragm30 which serves as a base plane, and of forming, over the diaphragm 30,an adhesive layer 401 with a material which will enhance adhesionbetween the diaphragm 30 and the lower electrode 403. Specific detailsare similar to the adhesive layer forming step (FIG. 2A) of Embodiment1.

This diaphragm may have a two-layer structure of silicon dioxide andzirconium oxide as shown in Embodiment 2. The manufacturing method andthe working-effect thereof are as stated in Embodiment 2.

Lower Electrode Forming Step (FIG. 13C):

This step is the step of forming, over the adhesive layer 401, a lowerelectrode 403 by using a conductive material.

A platinum film is formed with a thickness of, for example, 500 nm by asputtering film forming method over the surface of the adhesive layer401,. thereby forming the lower electrode 403.

Diffusion Preventing Layer Forming Step (FIG. 14A):

This step is the step of forming, over the lower electrode 403, adiffusion preventing layer 402 by using a material which will prevent aphenomenon of diffusion of a component of the adhesive layer 401 into apiezoelectric film 404 and which will also prevent a phenomenon ofdiffusion of a component of the piezoelectric film 404 into the lowerelectrode 403.

An iridium film 402 is formed with a thickness of about 20 nm over thesurface of the lower electrode 403 by means of, for example, asputtering method. Other than iridium, palladium, rhodium, ruthenium,osmium or the like may be used. To be accurate, this iridium layer andtitanium which has diffused from the adhesive layer due to the thermaltreatment at the time of baking of the piezoelectric film are alloyed,thereby forming the diffusion preventing layer 402 of the finalcomposition.

Piezoelectric Film Forming Step (FIG. 14B):

This step is the step of forming, over the diffusion preventing layer402, a piezoelectric film 404 by using a piezoelectric material.

The piezoelectric film 404 can be formed by a sol-gel method, asputtering method, a laser ablation method, a CVD method, an MOD methodor the like. Specific steps are similar to those of Embodiment 1.

Upon baking a piezoelectric precursor film, titanium which is theprincipal component of the adhesive layer 401 diffuses through the lowerelectrode 403 into the iridium layer 402. The diffused titanium depositsas titanium oxide at a grain boundary of iridium in the diffusionpreventing layer to form an alloy of iridium and titanium (Ir-Ti layer),thereby forming the diffusion preventing layer 402.

The diffusion preventing layer 402 where iridium and titanium arealloyed prevents titanium of the adhesive layer 401 from diffusing intothe piezoelectric film 404 and also prevents lead and oxygen in thepiezoelectric film 404 from diffusing into the lower electrode 403. Theinterface between the diffusion preventing layer 402 and thepiezoelectric film 404 has lattice matching at an atomic level, therebypreventing the generation of a low dielectric constant layer.Accordingly, it is possible to obviate the separation between thepiezoelectric film and the lower electrode, which may occur as a lowdielectric constant layer breaks upon the activation of thepiezoelectric device.

Upper Electrode Forming Step (FIG. 14C):

This step is the step of forming, over the piezoelectric film 404, anupper electrode 405 by using a conductive material. For example, iridiumis used as the conductive material to form, by the sputtering method,the upper electrode 405 with a thickness of about 100 nm.

The layer structure of the piezoelectric device 41 is completed throughthe above-described steps. In order to use it as the piezoelectricdevice, molding is performed by etching this layer structure in anappropriate shape. In order to manufacture an ink jet printing head,this layer structure of the piezoelectric device is molded into a shapeas a piezoelectric actuator and, at the same time, a structure necessaryfor the ink jet printing head is formed. Specific steps are similar tothose of Embodiment 1 and, therefore, descriptions thereof are omitted.

EXAMPLE 1

The piezoelectric device was formed by the manufacturing method of thisembodiment. FIG. 15 shows the results of measurement to see to whatdegree the diffusion preventing layer can prevent the diffusion oftitanium into the piezoelectric film at the time of baking of thepiezoelectric film. As shown in FIG. 15, the titanium content in thediffusion preventing layer was almost constantly about 50% with respectto the film thickness direction. The lower electrode contained almostconstantly about 5% titanium. It is apparent that titanium in theadhesive layer partly diffused through the lower electrode and thediffused titanium only partly remained in the lower electrode, and therest of the titanium and iridium were alloyed and remained in thediffusion preventing layer. Most of the titanium remained in theadhesive layer. It is confirmed that the diffusion preventing layer caneffectively prevent the diffusion of titanium into the piezoelectricfilm at the time of baking of the piezoelectric film.

An analysis was carried out on a composition ratio of Zr to Ti in thepiezoelectric film in this example. As a result, it was found that thecomposition ratio was the same as a synthesis ratio of the sol. It wasconfirmed that the diffusion preventing layer prevented the componentssuch as oxygen of the piezoelectric film from escaping.

FIG. 16 is a TEM photograph of the interface between the diffusionpreventing layer and the piezoelectric film of this example, which ismagnified 100,000 times. As can be seen from FIG. 16, titanium diffusedfrom the adhesive layer remained in the diffusion preventing layer anddid not diffuse into the piezoelectric film. It can be confirmed thatthe lattice arrangement at the interface between the piezoelectric filmand the diffusion preventing layer is matching and the piezoelectricfilm is oriented. It was confirmed that the method for manufacturing thepiezoelectric device of this invention would not impair thepiezoelectric properties of the piezoelectric film.

Subsequently, a withstand voltage of the piezoelectric device of thisexample was measured. As a result, the withstand voltage of aconventional product which did not comprise the diffusion preventinglayer was 50V, while the withstand voltage of the piezoelectric deviceof this example was 60V. It was confirmed that the withstand voltageenhanced by 20%.

EXAMPLE 2

The piezoelectric device was manufactured by the manufacturing method ofthis embodiment by changing the thickness of the lower electrode, thethickness of the piezoelectric film, the number of times of baking andso on. Table 3 shows the results of measurement of adhesive strengthbetween the lower electrode and the substrate in the piezoelectricdevice. However, a lamination structure of the manufacturedpiezoelectric device was a layer structure composed of the upperelectrode (Pt), the piezoelectric film (PZT), the diffusion preventinglayer (Ir-Ti), the lower electrode (Pt), and the substrate. As acomparison, a piezoelectric device having a layer structure without thediffusion preventing layer (the structure composed of the upperelectrode (Pt), the piezoelectric film (PZT), the lower electrode (Pt),the adhesive layer (Ti), and the substrate) was used.

TABLE 3 Film Thickness Thickness of Number of of Lower PiezoelectricTimes of Adhesive Electrode Film Baking strength Example 500 nm 0.8 μm 218.5 mN Comparison 500 nm 0.8 μm 2 17.8 mN Example 500 nm 1.2 μm 4 16.6mN Comparison 500 nm 1.2 μm 4 14.2 mN Example 300 nm 1.2 μm 4 12.2 mNComparison 300 nm 1.2 μm 4 9.8 mN

Table 4 shows the results of measurement of a breakdown voltage and apiezoelectric constant d₃₁ when the thickness of the piezoelectric filmof this example was changed.

TABLE 4 Thickness of Piezoelectric Breakdown Film Voltage d₃₁ at 15V d₃₁at 25V Example 0.8 μm 59V 198 pC/N 178 pC/N Comparison 0.8 μm 41V 178pC/N 161 pC/N Example 1.2 μm 91V 244 pC/N 197 pC/N Comparison 1.2 μm 62V191 pC/N 170 pC/N

As can be seen from Table 4, the breakdown voltage and the piezoelectricconstant d₃₁ of this example are larger than those of the comparison.This is because a low dielectric constant layer does not exist at theinterface between the lower electrode and the piezoelectric film in thepiezoelectric device of this example.

The value of the piezoelectric constant d₃₁ varies depending on themeasured voltage because there is a tendency of the piezoelectricconstant d₃₁ to decrease as the electric field becomes higher.Accordingly, it is effective to increase the thickness of thepiezoelectric film in order to enhance the properties of thepiezoelectric device. However, it is not desirable to make the thicknessof the piezoelectric film too large, because a displacement efficiencylowers. A desirable thickness of the piezoelectric film for an ink jetprinting head of high resolution is in the range of approximately 1 μmto 2 μm.

Since the diffusion preventing layer is provided in Embodiment 3, theappearance of a low dielectric constant layer can be prevented and thewithstand voltage of the piezoelectric device enhances. Since oxygendoes not escape from the piezoelectric film because of the diffusionpreventing layer, it is possible to prevent the separation between thepiezoelectric film and the lower electrode and it is possible to providea piezoelectric device, an ink jet printing head, and a printer whichhave long product-life cycles and which are highly reliable. Such apiezoelectric device can be activated at high frequencies. If an ink jetprinting head which comprises this piezoelectric device as apiezoelectric actuator is used, finer printing is possible.

Other Variations

This invention can be applied in many variations without limitation tothe respective embodiments described above. For example, thepiezoelectric device manufactured according to this invention is notlimited to the above-described manufacturing methods, but can be appliedto other manufacturing methods.

The layer structure of the piezoelectric device is not limited to thosedescribed above, and it is also possible to manufacture a piezoelectricdevice with a plurality of layer structures by complexing the steps.

The structure of the ink jet printing head is not limited to theabove-described structure, and a different structure may be employed aslong as it is of a piezo-jet ink jet type.

The piezoelectric film device of this invention is not limited to theuse as the piezoelectric device for the ink jet printing head asindicated in the above-described embodiments, and it can be applied tothe manufacture of: ferroelectric devices such as nonvolatilesemiconductor storage, thin film capacitors, pyroelectricity detectors,sensors, surface elasticity wave optical waveguides, optical storage,space light modulators, and diode laser frequency doublers; dielectricdevices; pyroelectricity devices; piezoelectric devices; andelectro-optic devices.

Industrial Applicability

Since this invention provides the diffusion preventing layer, it ispossible to prevent the state where impurities diffuse in the lowerelectrode at the time of baking of the piezoelectric film and, as aresult, the composition of the lower electrode becomes nonuniform.

Since this invention can maintain the orientation state of the lowerelectrode, it is possible to cause the piezoelectric film, which isformed over the lower electrode, to become oriented well, and to providethe piezoelectric device which exhibits superior piezoelectricproperties.

Since this invention can make the composition of the lower electrodeuniform in the thickness direction, the manufacture and designing becomeeasy, for example, when the lower electrode is used as the diaphragm.

According to this invention, it is possible to prevent the phenomenon ofdiffusion of the principal component of the adhesive layer through thelower electrode into the piezoelectric film at the time of baking of thepiezoelectric film, and to prevent the separation between the lowerelectrode and the piezoelectric film. Consequently, it is possible toprovide the piezoelectric device, the ink jet printing head and theprinter which are resistant to repeated fatigue caused when thepiezoelectric device is used as a piezoelectric actuator, and which aresuperior in durability and are highly reliable.

What is claimed is:
 1. A piezoelectric device exhibiting anelectromechanical transducing action, comprising: a lower electrode; anadhesive layer composed of a material which enhances adhesion between abase plane of the piezoelectric device and said lower electrode; adiffusion preventing layer formed between said adhesive layer and saidlower electrode, said diffusion prevention layer composed of a materialwhich prevents a phenomenon of diffusion of a component of said adhesivelayer into said lower electrode; a piezoelectric film formed over saidlower electrode, said piezoelectric film exhibiting theelectromechanical transducing action; and an upper electrode formed oversaid piezoelectric film.
 2. A piezoelectric device exhibiting anelectromechanical transducing action, comprising: an adhesive layer; alower electrode formed over the adhesive layer, wherein the adhesivelayer is composed of a material which enhances adhesion between a baseplane of the piezoelectric device and said lower electrode; a diffusionpreventing layer formed over said lower electrode; a piezoelectric filmformed over said diffusion preventing layer, said piezoelectric filmexhibiting electromechanical transducing action; wherein said diffusionlayer is composed of a material which prevents a phenomenon of diffusionof a component of the adhesive layer into the piezoelectric film andalso prevents a phenomenon of diffusion of a component of thepiezoelectric film into the lower electrode; and an upper electrodeformed over the piezoelectric film.
 3. A piezoelectric device accordingto claim 1 or 2, wherein the diffusion preventing layer is an alloy oftitanium and one device selected from a group consisting of iridium,palladium, rhodium, ruthenium, and osmium.
 4. A piezoelectric deviceaccording to claim 1 or 2, wherein the adhesive layer contains, as itsprincipal component, one device selected from a group consisting oftitanium and chromium.
 5. A piezoelectric device according to claim 1 or2, wherein the lower electrode is composed of platinum as its principalcomponent.
 6. An ink jet printing head comprising the piezoelectricdevice according to claim 1, as a piezoelectric actuator, over adiaphragm which serves as the base plane.
 7. An ink jet printing headaccording to claim 6, wherein the diaphragm has a laminated structure ofsilicon dioxide and zirconium oxide.
 8. A printer comprising the ink jetprinting head according to claim 6 as printing means.
 9. A method formanufacturing a piezoelectric device exhibiting an electromechanicaltransducing action, comprising the steps of: forming an adhesive layerover a base plane of the piezoelectric device; forming a diffusionpreventing layer over the adhesive layer; forming a lower electrode overthe diffusion preventing layer by using a conductive material; forming apiezoelectric film over the lower electrode by using a piezoelectricmaterial; and forming an upper electrode over the piezoelectric film byusing a conductive material, wherein the adhesive layer is formed with amaterial which enhances adhesion between the base plane and the lowerelectrode; and wherein said diffusion preventing layer is formed with amaterial which prevents a phenomenon of diffusion of a component of theadhesive layer into the lower electrode.
 10. A method for manufacturinga piezoelectric device exhibiting an electromechanical transducingaction, comprising the steps of: forming an adhesive layer over a baseplane of the piezoelectric device; forming a lower electrode over theadhesive layer by using a conductive material; forming a diffusionpreventing layer over the lower electrode with a material which preventsa phenomenon of diffusion of a component of the adhesive layer into thepiezoelectric film, and which also prevents a phenomenon of diffusion ofa component of the piezoelectric film into the lower electrode; forminga piezoelectric film over the diffusion preventing layer by using apiezoelectric material; and forming an upper electrode over thepiezoelectric film by using a conductive material, wherein the adhesivelayer is formed with a material which enhances adhesion between the baseplane and the lower electrode.
 11. A method for manufacturing apiezoelectric device according to claim 9 or 10, wherein the diffusionpreventing layer forming step is the step of forming the diffusionpreventing layer by using, as its principal component, one deviceselected from a group consisting of iridium, palladium, rhodium,ruthenium, and osmium as starting materials.
 12. A method formanufacturing a piezoelectric device according to claim 9 or 10, whereinthe adhesive layer forming step is the step of forming the adhesivelayer by using, as its principal component, one device selected from agroup consisting of titanium and chromium.
 13. A method formanufacturing a piezoelectric device according to claim 9 or 10, whereinthe lower electrode forming step is the step of forming the lowerelectrode by using platinum as its material.
 14. A method formanufacturing a piezoelectric device according to claim 9 or 10, whereinthe piezoelectric film forming step is the step including a thermaltreatment step.